With the increasing expansion of the Internet, existing IPv4 addresses composed of 32 bits are becoming insufficient. Accordingly, an IPv6 protocol employing an IP address of 128 bits appears to thoroughly solve the problem of insufficiency of the IPv4 addresses and to make significant improvements on address capacity, security, network management, mobility, quality of service, etc. Before the IPv6 protocol becomes the mainstream protocol, the IPv4 protocol will continue being used, thus the coexistence of the IPv4 network and the IPv6 network occurs. In addition, due to the imbalance of address allocation, some countries or regions still have enough IPv4 address space for allocation, and the IPv4 network will exist in these countries or regions for a long time. In the foreseeable future, the IPv4 network and the IPv6 network will coexist for quite some time.
The Internet Engineering Task Force (IETF) has established a specialized NGTRANS (Next Generation Transition) working group to study the problem of IPv4/IPv6 transition and efficient seamless intercommunication. Various transition technologies and intercommunication approaches have been developed at present. One of the typical transition technologies is dual protocol stack. The dual protocol stack technology is the most direct way to make IPv6 nodes compatible with IPv4 nodes, and the objects to be applied comprise communication nodes such as hosts and routers.
FIG. 1A shows a system intercommunicating by means of the dual protocol stack. An IPv4 protocol stack or an IPv6 protocol stack may be used for communication when an IPv4/IPv6 node 1 and an IPv4/IPv6 node 2 both supporting the dual protocol stack are intercommunicating. In the dual stack protocol technology shown in FIG. 1A, the nodes 1 and 2 supporting the dual stack protocol are allocated an IPv4 address and an IPv6 address by, for example, a dual protocol stack address server. In relation to the addresses used by the communication between dual stack nodes, IETF has suggested a default selection method for the nodes. In the method, a selected address (IPv4 or IPv6 address) is always used in the communication between two dual stack nodes, without the selected address being dynamically changed. The document RFC 3484 in the website www.ietf.org discusses the default address selection method in detail.
In the prior art, in order to solve the intercommunication problem between the IPv4 network and the IPv6 network, tunneling technology is also employed as the technology for transition from the IPv4 network to the IPv6 network. FIG. 1B is a schematic diagram showing the prior art in which the network intercommunication is made by means of the tunneling technology. In the tunneling technology, assuming an IPv6 node C accesses an IPv6 node D, after a IPv6 packet sent to the node D by the IPv6 node C arrives at a router X, a 6 over 4 IP packet is formed by the router X by encapsulating the IPv6 packet sent to the node D into an IPv4 packet whose destination address in the header is the IPv4 address of a router Y. The 6 over 4 packet is transmitted via the IPv4 network to the router Y, which removes the header of the IPv4 packet and transmits the IPv6 packet to the IPv6 node D via the IPv6 network. Therefore, the IPv6 packet can be transmitted over the IPv4 network by forming a tunneling path for transmitting the IPv6 packet between the routers X and Y. On the other hand, the IPv4 packet can be transmitted in a tunneling path of the IPv6 network by forming a 4 over 6 IP packet by encapsulating the IPv4 packet into the IPv6 packet.
However, in the above methods, bandwidth and router resource will be contended by IPv4 traffic and IPv6 traffic. In addition, a case where the IPv4 network is particularly busy while the IPv6 network resource is wasted might occur, and vice versa. In addition, in the prior art mentioned above, the network with lighter traffic cannot be selectively used for information transmission based on real-time traffic in the current network to utilize the network resource efficiently, since a fixed IPv4 address or IPv6 address is used when transmitting and receiving information between nodes communicating with each other, thereby using the corresponding IPv4 network or IPv6 network for information transmission. In particular, when the traffic in the IPv4 network is very heavy while the traffic in the IPv6 network is very light, or vice versa, the prior art cannot make real-time adjustments on the traffic in the two networks to improve the problem of utilization imbalance between the two networks.